Microtubules are present within the sensory ending of the numerous mechanoreceptors which function with cilia and modified cilia. We will use the campaniform sensillum, a ciliated mechanorecptor on the cockroach leg, as a model system for our studies. a) Transduction: The campaniform sensillum functions via a single bipolar neuron whose dendrite tip bears a modified cilium. The distal tip of the cilium is the sensory process, a membrane-limited bundle of 350-1500 parallel microtubules attached to the site of mechanical stimulation. We have shown that chemical disassembly of the sensory process microtubules is accompanied by a loss of sensory function of the campaniform sensillum. We want to find out (1) if sensory function is regained upon reassembly of the sensory process microtubules; (2) if the receptor potential is produced by the microtubules-packed sensory process; (3) if a quantitative relationship exists between the number of sensory process microtubules and the mechano- sensitivity of the campaniform, and (4) how much the mechanical stimulus must physically displace the sensory process in order to initiate electrical activity. b) Development: Insects periodically shed their skins during normal growth and development. Campaniform sensilla, like all external insect sense organs, are incorporated into the structure of the exoskeleton. We have shown that the microtubule-packed sensory process, which is coextensive with the exocuticle, is shed with the skin at the moult. We want to find out (1) how a new sensory process is elaborated, and (2) what morphologically detectable developmental events accompany the onset of bioelectric function in differentiating campaniform sensilla.